Su: 1.-.Third person of possesive . ("Yo fuí a su casa" it's mean "a la casa de ella", o de él). Or "Yo soy su empleado" = I am his employee 2.- Also....Second person of possesive, in an formal treat, respect...when we use "usted" instead of "tú" I am your employee = (with respect= "yo soy su empleado" ) =(with friendship= "yo soy tu empleado")

True, as Juan Carlos said, "su" means "your" in active phrases to express respect and good manners....

We use it to express that one thing belongs to one person (third person of singular and plural. Examples: Ella es Marta. Su casa es azul. Ellos son Ana y Juan. Su casa es roja.

"Su" is a third singular person´s possessive adjetive . We use it to express that one thing belongs to one person (third person of singular, masculine or femenine). Example: Yo rompí "su" juguete--> I broke his/her toy. Esta es su casa--> This is his/her home.